FR-A-2,581,559 describes a treatment plant for thickening a solid-liquid suspension, which operates continuously, placed at the delivery side of the sludge feed pump. This plant comprises a flat and stationary drainage or thickening grating, onto which the sludge that is to be thickened is continuously delivered, this sludge being constantly scraped by a scraping system with flexible blades. The sludge concentration increases gradually as it progresses along the grating zone.
This known plant, intended more specifically for thickening sludge from sewage works can be used either for final thickening, for example for an agricultural use of the sludge, or for pre-thickening, upstream of a dewatering plant.
Although, in general, this type of plant is satisfactory as it allows a broad range of sludge concentrations to be thickened, it does, however, have the drawback of operating with relatively low hydraulic flow rates, in particular in the case of low-concentration solid-liquid suspensions, that is to say ones which have concentrations of below 5 g/l. It is, incidentally, for this very reason that this known thickening plant is generally fed from a construction or an intermediate device whose function is to raise the concentration of the solid-liquid suspension fed to the plant.
Furthermore, this known plant is equipped with a grating made up of a number of large cross-section strips, the gaps percentage of which is of the order of 25%. This characteristic contributes to the hydraulic limitations of this type of plant.